Highly crystalline polypropylene with low xylene solubles

ABSTRACT

The invention is directed to a polypropylene resin which has a M w /M n  of less than 5, a melt flow rate of less than 7 g/10 min., a 1% secant flexural modulus of greater 5 than 300,000 psi and less than 2 wt. % xylene solubles.

“This application claims the benefit of U.S. Provisional ApplicationNos. 60/416,632, filed Oct. 7, 2002, and 60/491,586, filed Jul. 31,2003, which are both hereby incorporated by reference herein in theirentirety.”

FIELD OF THE INVENTION

This invention relates to highly crystalline propylene polymers having arelatively narrow molecular weight distribution (Mw/Mn), a relativelyhigh flexural modulus, and preferably a relatively low melt flow rate.More particularly, this invention is directed to a propylene homopolymerwhich has a low amount of xylene solubles, but also has a narrowmolecular weight distribution, retains a high flexural modulus and a lowmelt flow. The invention also relates to a blend of the above-describedhighly crystalline propylene homopolymer with an ethylene-alpha olefincopolymer. Preferably, the copolymer is comprised of units derived fromethylene and a C₄-C₈ alpha olefin.

BACKGROUND OF THE INVENTION

Broad molecular weight distributions have been thought to be necessaryto achieve a high flexural modulus to achieve stiffness. Broad molecularweight distributions, however, are associated with polymers having highmolecular weight fractions and low molecular weight fractions. The highmolecular weight fraction (sometimes referred to as a high molecularweight tail) can lead to increased die swell while processing thepolymer. This die swell will be especially pronounced for processes thatutilize low melt flow rate (MFR) polymers, especially fractional meltflow rate polymers. The low molecular weight fraction (sometimesreferred to as a low molecular weight tail) can lead to high xylenesolubles. Also, the low molecular weight fractions can cause processingproblems, such as die drip and smoking during polymer processing, aswell as environmental problems in the form of volatile organicemissions. Smoking is of particular concern with processes which utilizevery high melt flow rate polymers, such as fiber spinning and nonwovenfabrics production. Increasing melt flow rate has been associated withdecreasing molecular weight which decreasing molecular weight would beexpected to lower impact strength.

Additionally, lower molecular weight distribution has typically beenassociated with polypropylenes having lower stiffness, as measured byflexural modulus (see, for example, “Polypropylene Handbook”, E. P.Moore, pg. 243, Hanser/Gardner Publications, Cincinnati (1996)). What isdesired is a polypropylene that exhibits a relatively narrow molecularweight distribution, but also exhibits high flexural modulus and lowxylene solubles.

OBJECT OF THE INVENTION

An object of the invention is to provide a highly crystallinepolypropylene homopolymer having a narrow molecular weight distribution,low melt flow rate and high flexural modulus.

Another object of the invention is to provide a crystallinepolypropylene having a flexural modulus and molecular weightdistribution which are relatively insensitive to molecular weightchanges, but which also have low xylene solubles.

Still another object of the invention is to provide a polypropylenehomopolymer that provides the above properties and also exhibitsexcellent optical properties, such as improved contact clarity and lowervalues for haze than comparable commercially available polypropylenehomopolymers.

Another object of the invention is to provide for a highly crystallinepolypropylene that is a homopolymer or copolymer having less than 3percent (preferably less than 2 percent) by weight of units derived fromethylene and exhibits high flexural modulus, relatively narrow molecularweight distribution and excellent optical properties relative tocomparative commercially available polypropylene resin.

A further object of the invention is to provide an impact modifiedpolypropylene copolymer wherein the homopolymer (and/or copolymer)matrix has the above delineated properties and the impact modifiedpolypropylene copolymer exhibits an excellent balance of stiffness (asmeasured, for example, by flexural modulus and/or tensile strength) andtoughness (as measured, for example, by notched Izod impact tests) andfurther exhibits excellent optical properties relative to comparableimpact modified polypropylene copolymers having similar stiffness andtoughness.

Another further object of the invention is to provide a blend of highcrystalline polypropylene and high melt strength polypropylene thatprovides for articles having an excellent balance of toughness(including low temperature impact resistance), melt strength, stiffnessand clarity. In particular it is an object of the invention to provide ablend having the above listed properties together with an improvedability to be thermoformed under a wide variety of processingconditions.

These and other objects of the invention will become apparent withreference to the specification.

SUMMARY OF THE INVENTION

In one aspect, the invention is a polypropylene resin which has a lowmelt flow rate, a narrow molecular weight distribution (M_(w)/M_(n)) andlow xylene solubles. Heretofore, it has been thought that broadmolecular weight distributions were necessary to attain high stiffnessand modulus. Broad molecular weight distributions, however, can resultin unacceptably high xylene solubles, especially for polymers havinghigher melt flow rates, because of low molecular weight polymerfractions present in the resin. These solubles result in processing andenvironmental problems which have to be addressed. Additionally, broadmolecular weight distributions result in an unacceptable high percentageof high molecular fraction material for lower melt flow rate polymers.As discussed earlier, these high molecular weight fractions result inincreased die swell and other processing problems for lower melt flowrate polypropylene polymers.

In this aspect, the polypropylene resin of the invention provides ahighly crystalline resin having a crystallinity of greater than 70%(preferably greater than 73%, more preferably greater than 75%), a lowmelt flow rate (MFR) of less than 7 g/10 minutes at 230° C./2.16 kg, aM_(w)/M_(n) of less than 5, a 1% secant modulus of greater than 300,000p.s.i. and xylene solubles of less than 2 percent by weight (wt %),preferably less than 1 wt %. Preferably, the polypropylene resin isnucleated/clarified with a nucleator/clarifier additive, and has a hazeof less than 30% (more preferably less than 25%, most preferably lessthan 20%), a crystallization temperature of greater than 130° C.,preferably greater than 133° C. In an important aspect, thepolypropylene resin of the invention has a melt flow rate at 230° C. ofless than 5 g/10 min, an isotactic pentad/triad ratio of preferablygreater than 95%, more preferably greater than 96%, further morepreferably greater than 98%, most preferably greater than 99%, and apentad isotacticity of preferably at least 96%, more preferably at least97%, most preferably at least 98%.

In a second aspect, the polypropylene resin is defined by the followingequation:FM/((XS−0.74% E)*MWD)≧30,000 p.s.i.  (1)wherein XS≦2 wt %+% E; and

-   -   MWD≦6; and        Where FM is the 1% secant flexural modulus measured in        accordance with procedure ASTM D790-00, XS is weight percent of        the xylene soluble content of the resin measured in accordance        with the procedure described below, and MWD is defined as Mw/Mn.        % E is the weight percent of units derived from ethylene in the        polypropylene. Preferably, the MWD of the polypropylene        homopolymer is less than 5.5, more preferably less than 5.        Preferably the XS≦2 wt %+% E/2. In this aspect, the        polypropylene resins preferably are nucleated/clarified with a        nucleator/clarifier additive.

In one embodiment of this second aspect, the polypropylene resin is ahomopolymer. In this embodiment, the haze values exhibited by thenucleated/clarified resins are preferably less than 30%, more preferablyless than 25%, most preferably less than 20% as measured in accordancewith procedure ASTM D1003. The isotactic pentad/triad ratio ispreferably at least 95%, more preferably at least 98%, most preferablyat least 99%. Additionally, the crystallinity of the inventive resins ispreferably at least 70%, more preferably at least 73%, most preferablyat least 75%, as measured in accordance with the description describedbelow. Further, the inventive polypropylene has crystallizationtemperature of greater than 130° C., preferably greater than 133° C.

In another embodiment of this second aspect, the polypropylene resin isa propylene-based copolymer having 3% or less by weight units derivedfrom ethylene, preferably 2% or less by weight, more preferably 1% orless by weight units derived from ethylene; and where modulus isespecially important, preferably from 0.2% by weight to 0.8% by weightunits derived from ethylene. Preferably, the haze exhibited by theseresins is 25% or less, more preferably 20% or less, and for copolymerswith 2 to 3% by weight units derived from ethylene, preferably hazevalues of 15% or less. Preferably, the resins exhibit Pentad/triadratios of at least 98.0%, preferably at least 98.5% and in some instancepentad to triad ratios of at least 99.0%. Furthermore, the crystallinityexhibited by these copolymer resins as measured by DSC (as describedbelow) is preferably at least 55%, more preferably at least 60%, furthermore preferably at least 65%. In this embodiment the pentad isotacticityis at least 90%, preferably at least 92%, more preferably at least 94%,most preferably at least 95%, and in some instances at least 96%.Preferably, in this embodiment the XS content is preferably less than 4percent by weight, more preferably less than 3 percent by weight,further more preferably less than 2 percent by weight of thepolypropylene resin. Additionally, for the inventive polymers, it hasbeen unexpectently discovered that the polymers have a comparable orlower melting point (as determined by DSC) together with highercrystallinity for a given weight percent of units derived from ethylene.This characteristic of the resins will lead to more efficient and facilemelt processing than conventional Ziegler-Natta propylene-basedcopolymers. Furthermore, in this embodiment of the second aspect, theinventive polymers exhibit a relationship where the value obtained fromequation (1) is preferably greater than 40,000 p.s.i.

In a third aspect, the invention is an impact modified polypropylenecopolymer composition comprised of a first polymer component comprisinga high crystalline homopolymer or copolymer resin in accordance with thefirst and/or second aspect of this invention. This high crystallineresin is blended with an impact modifier. The impact modifier improvesthe toughness and impact strength of the composition. The impactmodifier preferably is a polyolefin rubber, which exhibits a glasstransition temperature of less than −20° C. The impact modifierpreferably makes up no greater than 40% by weight of the composition.

The impact modifiers include ethylene/alpha-olefin copolymers andterpolymers and block copolymers, ethylene-propylene diene rubbers,propylene-alpha olefin copolymers, silicon rubbers, butadiene-basedrubber and the like. The more preferred impact modifiers areethylene/alpha-olefin copolymers made with single-site or metallocenecatalysts wherein the units within the impact modifier derived fromethylene are greater than 50% by weight and the alpha-olefin is selectedfrom olefins having at least three carbon atoms, preferably at least 4carbon atoms, more preferably from 4 to 12 carbon atoms, further morepreferably from 4 to 8 carbon atoms. The even more preferredalpha-olefins are 1-butene, 1-hexene, 1-heptene, and 1-octene. The mostpreferred alpha-olefin is 1-octene.

The impact modifiers preferably have a density of from 0.854 to 0.91g/ml. For ease of handling, the impact modifier preferably has a densitygreater than 0.865 g/ml. In applications requiring greater impact, theimpact modifier preferably has a density of from about 0.865 g/ml to0.88 g/ml. For applications requiring enhanced clarity, the impactmodifier preferably has a density of from 0.885 g/ml to 0.91 g/ml. Whereclarity is critical, preferably the density of the impact modifier ismatched to the density of the high crystalline polypropylene homopolymeror copolymer. In order to be matched, the density of the impact modifieris preferably within 0.03 g/ml of the density of the high crystallinepolypropylene, more preferably within 0.02 g/ml, most preferably within0.01 g/ml of the density of the high crystalline polypropylene used.

In a further aspect, a high crystalline polypropylene resin, asdescribed above is blended with a high melt strength polypropylene (asdescribed below) to provide a blend having an excellent balance of lowtemperature impact resistance, improved melt strength (relative tocomparable blends not containing a high melt strength polypropylene),stiffness, and optical properties, such as clarity.

BRIEF DESCRIPTION OF THE FIGURE

The FIGURE is a graph showing the 1% secant flexural modulus exhibitedby the inventive high crystalline propylene-ethylene copolymers (HC-RCP)versus the flexural modulus for comparative conventional Ziegler-Nattapropylene-ethylene copolymers (RCP). The FIGURE shows that for ethylenelevels of 3% or less, the inventive copolymers are stiffer thanconventional propylene-ethylene copolymers. The data for FIG. 1 comefrom the resins of Examples 2, and 7-10 and Comparative 7, 10a, and 10bthat were tested in accordance with ASTM D790-00, except that they wereaged for two weeks.

DETAILED DESCRIPTION OF THE INVENTION

Degree of crystallinity is measured by differential scanning calorimetry(DSC) using a Q1000 TA Instrument. In this measurement a small tenmilligram sample of the propylene polymer is sealed into an aluminum DSCpan. The sample is placed into a DSC cell with a 25 centimeter perminute nitrogen purge and cooled to about minus 100° C. A standardthermal history is established for the sample by heating it at 10° C.per minute to 225° C. The sample is kept at 225° C. for 3 minutes toensure complete melting. The sample then is cooled at 10° C. per minuteto about −100° C. The sample is again kept isothermal at −100° C. for 3minutes to stabilize. It is then reheated at 10° C. per minute to 225°C. The observed heat of fusion (ΔH_(observed)) for the second scan overa range of 80-180° C. is recorded. The observed heat of fusion isrelated to the degree of crystallinity in weight percent based on theweight of the polypropylene sample by the following equation:Crystallinity %=(ΔH_(observed))/(ΔH_(iotactic pp))×100  (2)where the heat of fusion for isotactic polypropylene (ΔH_(iotactic pp))is reported in B. Wunderlich, Macromolecular Physics, Volume 3, CrystalMelting, Academic Press, New York, 1960, p 48, is 165 Joules per gram(J/g) of polymer. The peak temperature of crystallization from the meltis determined by the DSC as above with a cooling rate of 10° C./min. Themelting temperature is determined by the peak of the melting transition.

Molecular weight distribution (MWD) for the polypropylene homopolymersis determined by gel permeation chromatography (GPC) as follows:

The polymers are analyzed by gel permeation chromatography (GPC) on aPolymer Laboratories PL-GPC-220 high temperature chromatographic unitequipped with four linear mixed bed columns, 300×7.5 mm (PolymerLaboratories PLgel Mixed A (20-micron particle size)). The oventemperature is at 160° C. with the autosampler hot zone at 160° C. andthe warm zone at 145° C. The solvent is 1,2,4-trichlorobenzenecontaining 200 ppm 2,6-di-t-butyl-4-methylphenol. The flow rate is 1.0milliliter/minute and the injection size is 100 microliters. A 0.2% byweight solution of the sample is prepared for injection by dissolvingthe sample in nitrogen purged 1,2,4-trichlorobenzene containing 200 ppm2,6-di-t-butyl-4-methylphenol for 2.5 hrs at 160° C. with gentle mixing

The molecular weight determination is deduced by using ten narrowmolecular weight distribution polystyrene standards (from PolymerLaboratories, EasiCal PS1 ranging from 580-7,500,000 g/mole) inconjunction with their elution volumes. The equivalent polypropylenemolecular weights are determined by using appropriate Mark-Houwinkcoefficients for polypropylene (as described by Th. G. Scholte, N. L. J.Meijerink, H. M. Schoffeleers, and A. M. G. Brands, J. Appl. Polym.Sci., 29, 3763-3782 (1984), incorporated herein by reference) andpolystyrene (as described by E. P. Otocka, R. J. Roe, N. Y. Hellman, P.M. Muglia, Macromolecules, 4, 507 (1971) incorporated herein byreference) in the Mark-Houwink equation:{η}=KM^(a)where K_(pp)=1.90E-04, a_(pp)=0.725 and K_(ps)=1.26E-04, a_(ps)=0.702.

Unless otherwise indicated, for the propylene-based resins listedherein, 1% Secant flexural modulus is determined by ASTM D790-00.

Melt flow rate is measured in accordance with ASTM D 1238-01 test methodat 230° C. with a 2.16 kg weight for the propylene-based polymers. Meltindex for the ethylene-based polymers is measured in accordance withASTM D 1238-01 test method at 190° C. with a 2.16 kg weight.

Xylene solubles are determined by dissolving 4±0.1000 g. of sample intoa 250 ml Erlenmeyer flask and adding by means of a pipette 200 ml ofinhibited xylene. To inhibit xylene, add 18.35 g of Irganox 1010 to 200mls. of xylene in a beaker and stir until dissolved. After the Irganox1010 is dissolved, pour the solution into a 4.9 gallons of xylene andthoroughly mix the solution. Introduce a stirring bar, place awater-cooled condenser on the flask and position the flask assembly on amagnetic stirrer/hot plate. Stir vigorously and adjust heating to obtaingentle boiling until the sample is completely dissolved. A nitrogenblanket should be maintained on the condenser during the procedure.After the sample is dissolved, remove the flask assembly from themagnetic stirrer/hot plate, remove the stirring bar, then cover. Let theflask cool to near room temperature (30° C., cooling takes approximately1 hour). Place a lead ring on the flask and immerse in constanttemperature water bath. After temperature inside flask reaches 25±0.5°C., let stand in water 30 more minutes. During the cooling, theinsoluble portion precipitates. The solution is filtered; then a 100 mlaliquot of the filtrate is placed in an aluminum pan and evaporated todryness under a nitrogen stream. The solubles present are determined byweighing the residual polymer.

Isotactic pentad percent, Isotactic triad percent and the Isotacticpentad/triad ratio are determined by one of ordinary skill in the artaccording to the following: ¹³C nuclear magnetic resonance (NMR)provides a direct measure of the tacticity of poly(propylene)homopolymers. The analysis used here neglects chain ends and inverseinsertions.

The FIGURE below shows the typical polypropylene triads and theirassociated ¹³C chemical shifts. For the triad names (mm, mr, and rr) ‘m’stands for meso, and ‘r’ stands for racemic. The isotactic triad percentis a measure of the mm triads.

The isotactic pentad percent is a measure of the mmmm pentads Thechemical shift for mmmm pentads is 22.0-21.7 ppm.

V. Busico, R. Cipullo, G. Monaco, M. Vacatello, A. L. Segre,Macromolecules 1997, 30, 6251-6263 describes methods for determiningisotactic pentad and triads using NMR analysis.

The isotactic pentad/triad ratio is the ratio of the isotactic pentadpercent to the isotactic triad percent. In determining the isotacticpentad and triad values, the samples are prepared by dissolving 0.5 g ofthe polypropylene homopolymer in a mixture of 1.75 g oftetrachloroethane-d2 (TCE-d2) and 1.75 g of 1,2-orthodichlorobenzene.Samples are homogenized in a heating block at 150° C. and heated with aheat gun to facilitate mixing. NMR experiments are performed on a VarianUnity+400 MHz, at 120° C., using a 1.32 sec acquisition time, 0.7 secrepetition delay, 4000 acquisitions and continuous proton decoupling(fm-fm modulation), with and without spinning the sample. Total scantime used is 2.25 hrs.

The reactor configuration to make the crystalline polypropylene is onewhich does not broaden the molecular weight distribution beyond thetarget value. Suitable reactors include a liquid pool reactor with astirred tank, a gas phase fluidized bed reactor, a single continuousstirred tank reactor, and a single slurry loop reactor with high monomerfeed to internal recirculation ratio. These types of reactors may beused in combination if the reactants are properly controlled to minimizebroadening of the molecular weight distribution for the crystallinepolypropylene produced, usually by maintaining constant hydrogenconcentration from one reactor to the next.

The additive package which is used for the polypropylene includes theadditives typically used for propylene polymers. Additionally, anucleator/clarifier additive is preferably used to increase the flexuralmodulus of the resulting resin. This nucleator/clarifier is chosen tooptimize the stiffness/toughness/clarity balance. Any additive, whichsimultaneously clarifies and nucleates can be used. Nucleator/clarifieradditives such as ADK NA-11 and ADK NA-21 are commercially availablefrom Asahi Denka Kokai and preferably are added to the crystallinepolypropylene of the invention to improve thestiffness/toughness/clarity balance of the resins. Millad 3988 availablefrom Milliken & Company is another example of a Nucleator/Clarifier. TheNucleator/Clarifier is preferably present within the polypropylene atlevels of at least 500 ppm and less than 2500 ppm; more preferably thenucleator/clarifier is at levels of at least 650 ppm and less than 1500ppm; most preferably the nucleator/clarifier is at levels of at least750 ppm and less than 1250 ppm. In some applications where cystallinityis particularly important, the nucleator/clarifier is most preferablypresent at levels of up to 1500 ppm. Nucleator/Clarifiers are preferablyadded to the crystalline polypropylene of the invention to improve thestiffness/toughness/clarity balance of the resins.

A Ziegler-Natta catalyst (a ZN catalyst) combined with a suitableinternal/external donor combination that will produce a polypropyleneproduct with xylene extractables or solubles of less than of 2 wt %, asmeasured by the method described above, and a NMR pentad/triad ratio ofpreferably greater than 95%, more preferably greater than 98%, mostpreferably at least 99%.

The polypropylene resins and the impact modified polypropylenecopolymers of the invention are useful for the fabrication of articlesvia (extrusion or injection) blow molding, injection molding, injectionstretch blow molding, rotomolding, profile extrusion, sheet extrusion,pipe extrusion, thermoforming, blown and cast film forming, and foaming.

In particular, the polypropylene resins and the impact modifiedpolypropylene copolymers are especially useful for making articles byprocesses that require relatively low melt flow rates, such as, BOPPfilm and blown film processes, blow molding and profile extrusion (suchas pipe extrusion) processes, thermoforming and calendering processes,all of which take advantage of polymers having melt flow rates of 5 orbelow, preferably, 4 or below. Additionally, the superior stiffness ofarticles made from the homopolymer polypropylene and impact modifiedpolypropylene copolymer resins of the invention will lead to enhancedprocessability, and will enable the articles to be downgauged inthickness, which will lead to reduced manufacturing cycle time andreduced costs. Further, the impact modified polypropylene copolymerresins of the invention will provide enhanced low temperature toughnessto articles made with it. Further, the impact modified polypropylenecopolymers of the invention will also exhibit excellent heat distortioncharacteristics, due to their high crystallization temperatures and highmelting point temperatures.

Some examples of end-use application that the resins are suitable forinclude: deli containers, microwavable containers, frozen foodcontainers, trays for holding food, dairy containers, meat and poultrycontainers and trays, lidstock, cups, bowls, and food containers, ingeneral.

In a particular aspect, the high crystalline polypropylene is blendedwith a high melt strength polypropylene. The high melt strengthpolypropylene preferably is made through the use of a coupling agent asdescribed in U.S. Pat. No. 6,472,473 B1 to Ansems et. al, issued Oct.29, 2002, which is incorporated by reference herein in its entirety.Preferably, the coupling agent is a poly(sulfonyl azide) as described inU.S. Pat. No. 6,472,473 B1. In this aspect the high melt strengthpolypropylene may be homopolymer polypropylene, a propylene-basedcopolymer or an impact modified propylene-based copolymer blend.Preferably, the high melt strength polypropylene is a coupled impactpropylene copolymer as described in U.S. Pat. No. 6,472,473 B1.

In this aspect, the weight ratio of high crystalline polypropylene tohigh melt strength polypropylene typically is from 95:1 to 1:95,preferably from 19:1 to 7:3. The blend of this aspect will provideexcellent processing properties as compared with blends that don'tcontain a high melt strength polypropylene, including: broadenedprocessing temperature window, reduced sag in articles duringthermoforming applications, improved wall thickness uniformity in thefinal articles, and increased processing speeds during articleformation. Further, as discussed earlier, the produced articles willalso exhibit an excellent balance of toughness, stiffness and opticalproperties, such as contact clarity.

The end-use articles, which can take advantage of the blend of thisaspect, are those described earlier. In particular, the blends of thisaspect will be especially useful for thermoforming processes. Forthermoforming, the melt flow rate of the blend is typically from 0.1 to6 g/10 min, preferably from 0.5 to 4 g/10 min.

EXAMPLES Example 1

A polypropylene homopolymer, Example 1, Tables 1 and 2, is produced in asingle, continuous bulk phase (condensed propylene) stirred tankreactor. A Ziegler-Natta catalyst, which includes a titanium catalyticactive metal species supported on a magnesium chloride support, which iscommercially available as Toho Series C, Group JC and may be purchasedfrom Toho Titanium Ltd., is suspended in Kaydol white mineral oil,purchased from Witco, at 38 wt. % and stored in a stirred catalyst feedtank. The suspended catalyst is pumped directly into a nominal 25,000gallon continuous, stirred tank reactor which is filled to approximately⅔ capacity with liquid propylene. The desired temperature of the reactoris 65-68° C. controlled by condensing propylene vapor in a separate setof heat exchangers and returning the liquid stream to the reactor alongwith the non-condensable fraction. An external alkoxysilane donor, whichis commercially available from Degussa-Huels, [(CH₂)₄CH]₂Si(OMe)₂, isfed continuously to the reactor in the amount needed to reduce thexylene extractable fraction to less than 1%, measured as describedabove. For all the propylene resins listed herein the xylene solublestest described above was used to measure the xylene soluble fraction.The target concentration of the external donor in the liquid propylene,corrected for solids, is 150 ppm. Undiluted aluminum alkyl cocatalysts,(triethylaluminum, AlEt₃ commonly called TEAL) are added to thepropylene feed stream to adjust the TEAL concentration in the liquidpropylene to a control target of 150 ppm in the liquid propylene. Apolypropylene polymerization is conducted with the reactor polymersolids at about 40-42 wt. %. A chain transfer agent, hydrogen, iscontinuously fed to the reactor, to produce a 1 g/10 min MFR propylenepolymer, as measured by ASTM D 1238-01. The reactor discharge stream isdegassed in a series of three vessels to separate the liquid propyleneand process lights from the polypropylene powder product. The degassedpowder then is forwarded to a ribbon blender/heater in 4000 lb. batches.A nucleator/clarifier additive or agent ADK NA-11, which is a complexorganophosphate metal salt, is commercially available from AmfineChemical Corp., the North American joint venture of Asahi Denka KogyoK.K. and Mitsubishi Corp. Antioxidants Irgafos™ 168,Tris(2,4-di-t-butylphenyl) phosphite, and Irganox™ 1010,Tetrakismethylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate) methane, iscommercially available from CIBA Specialty Chemical. The ADK NA-11 at1500 ppm, DHT-4A at 400 ppm, Irgafos 168 at 1000 ppm and Irganox 1010 at1000 ppm are added to the ribbon blender and mixed. DHT-4A is ahydrotalcite-like compound, Mg_(4.3)Al₂(OH)_(12.6)CO₃-mH₂O, that hasbeen developed as a stabilizer (halogen scavenger) for polyolefin andother plastics. DHT-4A is sold commercially by Kyowa Chemical IndustryCo., Ltd. The polypropylene powder then is dumped into a surge vessel.The powder then is continuously fed to a set of single screw extrudersfor compounding and pelletization. This product homopolymer is producedand placed in a rail car hopper. In addition to the properties of Tables1 and 2, the resin of Example 1 exhibited a 1% Secant Flexural Modulusof 374,000 p.s.i. after being aged for 2 weeks under the conditions setforth in ASTM D790-00. It can be seen from this Example and thefollowing Examples, that the inventive propylene-based resins exhibitedexcellent flexural modulus properties equivalent to or better than thecomparable conventional Ziegler-Natta polymers, while at the same timeexhibiting better optical properties (such as haze) for a given modulus.It is significant that this excellent balance of stiffness and opticalproperties is achieved with a relatively low Mw/Mn (molecular weightdistribution).

Example 2

A polypropylene homopolymer of Example 2, Tables 1 and 2, is produced inthe same manner as Example 1, except that a chain transfer agent,hydrogen, is continuously fed to the reactor to produce a 4.5 g/10 minMFR polypropylene polymer. In addition to the properties of Tables 1 and2, the resin of Example 2 exhibited a 1% Secant Flexural Modulus of385,000 p.s.i. after being aged for 2 weeks under the conditions setforth in ASTM D790-00.

Example 3

A polypropylene homopolymer of Example 3, Tables 1 and 2, is produced inthe same manner as Example 1, except that a chain transfer agent,hydrogen, is continuously fed to the reactor to produce a 20 g/10 minMFR polypropylene polymer. Trigonox™ 101, 2,5-Dimethyl-2,5di(t-butylperoxy)-hexane (a polypropylene cracking agent), purchasedfrom Akzo Nobel is added to the ribbon blender before pelletization. Inaddition to the properties of Tables 1 and 2, the resin of Example 3exhibited a 1% Secant Flexural Modulus of 375,000 p.s.i. after beingaged for 2 weeks under the conditions set forth in ASTM D790-00.

Example 4

A polypropylene homopolymer of Example 4, Tables 1 and 2, is produced inthe same manner as Example 1, except that a chain transfer agent,hydrogen, is continuously fed to the reactor to produce a 2.1 g/10 minMFR impact modified polypropylene copolymer final product. The aimtarget MFR for the homopolymer is 1.6 g/10 min MFR. The MFR and otherproperties of this intermediate homopolymer were not measured, but theproperties of the homopolymer are expected to be similar to theproperties of the homopolymer of Example 1. The copolymer final productis made by introducing 18% by weight of a commercial rubber Affinity™ PL1880, an ethylene/1-octene polyethylene copolymer having a melt index(I₂) of 0.75-1.25 g/10 min, a density of 0.8995-0.9045 g/ml, and anI₁₀/I₂ of 8.5-9.5 available from The Dow Chemical Company, along withthe other named additives into the ribbon blender, and then mixed. Themixture of polypropylene powder and polyethylene pellets then is dumpedinto a surge vessel. The mixture then is continuously fed to a set ofsingle screw extruders for compounding and pelletization. The impactmodified polypropylene is produced and placed in a rail car hopper.

The impact modified polypropylene polymer had the following propertiesin addition to those listed in Tables 1 and 2:

Notched Izod, 73 deg. F., ft-lb/in: No Break

Gardner Impact Resistance, 73 deg. F., ft-in: 280

Distortion temperature under load, 66 psi, deg. F.: 235° F. (measured inaccordance with ASTM D 648-98c).

This Example shows that through the use of a highly crystallinepolypropylene homopolymer as a starting material, an impact modifiedpolypropylene copolymer can be obtained that exhibits an excellentstiffness/toughness/clarity balance. Preferably, the impact modifiedcopolymers have a 1% secant flexural modulus of at least 200,000 p.s.i.,more preferably at least 220,000 p.s.i., further more preferably atleast 235,000 p.s.i., most preferably at least 240,000 p.s.i., and insome instances, at least 250,000 p.s.i. Additionally, the impactmodified polypropylene copolymers of the invention preferably exhibit“no break” IZOD levels at room temperature and at 0° C.; and preferablyexhibit a ductile to brittle transition temperature (DBTT) of less than10° C., more preferably less than 0° C., further more preferably lessthan −5° C., and in some instances less than −10° C., even morepreferably less than −20° C. Further, the impact modified polypropylenecopolymers preferably exhibit haze levels less than 30%, more preferablyless than 25%, further more preferably less than 23%, and in someinstances less than 21%.

Examples 5 and 6 show the properties of an inventive polypropylenehomopolymer and impact modified polypropylene copolymer that contain 830ppm of ADK NA-11. These examples show that very similar physicalproperties can be obtained while using a lower amount ofnucleator/clarifier.

Example 5

A polypropylene homopolymer of Example 5, Tables 1 and 2, is produced inthe same manner as Example 1, except that a chain transfer agent,hydrogen, is continuously fed to the reactor to produce a 1.5 g/10 minMFR polypropylene polymer. Also, as discussed earlier, 820 ppm to 830ppm of ADK NA-11 nucleator/clarifier is used in the polymer of thisExample.

Example 6

An impact modified polypropylene copolymer of Example 6, Tables 1 and 2,is produced in the same manner as Example 4, except that, as discussedearlier, 820 ppm of ADK NA-11 nucleator/clarifier is used in the polymerof this Example. The crystallinity of the intermediate homopolymer wasnot measured, but the value of crystallinity is expected to be similarto the values for the homopolymer of Example 1, possibly lower by about1%. However, the values for melting point temperature, crystallizationtemperature and flexural modulus were measured and were found to be asfollows: (1) the melting point will be reduced by no greater than 1° C.,(2) the crystallization temperature is unchanged, and (3) the 1% secantflexural modulus is reduced by about 4000 p.s.i. compared to the valuesprovided for the homopolymer of Example 1.

The impact modified polypropylene polymer of Example 6 had the followingproperties in addition to those listed in Tables 1 and 2:

Notched Izod, 73 def F, ft-lb/in: 10.5 ft-lb/in;

Distortion temperature under load, 66 psi, deg. F.: 240° F. (measured inaccordance with ASTM D 648-98c); and

Tensile Strength at yield, in accordance with ASTM D 638-99 of 5100 psi.

Example 7a

A copolymer of ethylene and propylene, Example 7a, Tables 1 and 2, isproduced in a single, continuous bulk phase (condensed propylene) loopreactor. A Ziegler-Natta catalyst, which includes a titanium catalyticactive metal species supported on a magnesium chloride support, which iscommercially available as Toho series C, group JC, is suspended inKaydol white mineral oil, available from Witco, and stored in a stirredcatalyst feed tank. The suspended catalyst is pumped directly into anominal 150 gallon continuous, pumped loop reactor. The desiredtemperature of the reactor is 70-76° C., controlled with an externalcooling jacket on the loop reactor. An external alkoxysilane donor,which is commercially available from Degussa-Huels, [(CH₂)₄CH]₂Si(OMe)₂(and is often referred to as D-Donor) diluted with hexane as appropriateto facilitate flow control, is fed continuously to the reactor in theamount needed to reduce the xylene extractable fraction to less than 1%,measured as described above. The target concentration of the externaldonor in the liquid propylene, corrected for solids, is 150 ppm.Aluminum alkyl cocatalysts diluted with hexane as appropriate tofacilitate flow control, (triethylaluminum, AlEt₃ commonly called TEAL)are added to the propylene feed stream to adjust the TEAL concentrationin the liquid propylene to a control target of 150 ppm in the liquidpropylene.

A random co-polymerization of ethylene and propylene is conducted withthe reactor polymer solids ranging from 20-45 wt. %. Ethylene iscontinuously fed to the reactor with the propylene to achieve a targetof 0.5 percent by weight units derived from ethylene. A chain transferagent, hydrogen, is continuously fed to the reactor, to produce a 3 g/10min MFR propylene copolymer, as measured by ASTM D 1238-01. The reactordischarge stream is degassed in a vessel to separate the liquidpropylene and process lights from the polypropylene powder product. Thedegassed powder then is continuously forwarded to a Hosokawa Bepex TorusDisc heat exchanger and then to a purge column where counter flow ofhumidified nitrogen removes residual monomer. Reactor powder iscollected in boxes and sent to a separate compounding facility.

A nucleator/clarifier additive or agent Millad 3988 available fromMilliken & Company, Antioxidants Irgafos™ 168,Tris(2,4-di-t-butylphenyl) phosphite, and Irganox™ 1010,Tetrakismethylene(3,5-di-t-butyl-4-hydroxyhydrocinnamate) methane, whichis commercially available from CIBA Specialty Chemical. DHT-4A is ahydrotalcite-like, Mg_(4.3)Al₂ (OH)_(12.6)CO₃-mH₂O, compound that hasbeen developed as a stabilizer (halogen scavenger) for polyolefin andother plastics. DHT-4A is sold commercially by Kyowa Chemical IndustryCo., Ltd. The Millad 3988 at 500 ppm, DHT-4A at 400 ppm, Irgafos 168 at1000 ppm and Irganox 1010 at 1000 ppm are fed along with the reactorpowder to a Century 40 mm twin screw extruder, pelletized and placedinto boxes.

Example 7b

A copolymer of ethylene and propylene, Example 7b, Tables 1 and 2, isproduced in the same manner as Example 7a, except that ADK NA-11 iscompounded into the resin at 2000 ppm using a ZSK 30 mm twin screwextruder.

Example 8

A copolymer of ethylene and propylene, Example 8, Tables 1 and 2, isproduced in the same manner as Example 7b, except that ethylene iscontinuously fed to the reactor to produce a target 1.5 wt. % ethyleneco-polymer.

Example 9

A copolymer of ethylene and propylene, Example 9, Tables 1 and 2, isproduced in the same manner as Example 7b, except that ethylene iscontinuously fed to the reactor to produce a target 2 wt. % ethyleneco-polymer.

Example 10

A copolymer of ethylene and propylene, Example 9, Tables 1 and 2, isproduced in the same manner as Example 7b, except that ethylene iscontinuously fed to the reactor to produce a target 3 wt. % ethyleneco-polymer.

Examples 7a-10 show that the propylene-based copolymers of the inventionhave an excellent balance of flexural modulus and optics compared toconventional Ziegler-Natta propylene-based copolymers. This is furtherillustrated by the FIGURE, which shows that the inventivepropylene-based copolymers exhibit better modulus than conventionalZiegler-Natta propylene-ethylene copolymers at ethylene levels of 3% byweight or less.

COMPARATIVE EXAMPLE Comparative Example 1

A commercial homopolymer product of Basell, T2101F, Tables 1 and 2,which has a broad molecular weight distribution.

Comparative Example 2

A commercial product of Amoco, 9433, Tables 1 and 2, which has a broadmolecular weight distribution.

Comparative Example 3

A commercial product of Basell, V2400G, Tables 1 and 2, which has abroad molecular weight distribution.

Comparative Example 7

A commercial product available from The Dow Chemical Company under thetrade name H308-02Z, Tables 1 and 2, which has been compounded with anadditional 2000 ppm of ADK NA 11.

Comparative Example 10a

A commercial product available from The Dow Chemical Company under thetrade name 6D69, Tables 1 and 2, which has been compounded with anadditional 2000 ppm of ADK NA 11.

Comparative Example 10b

A commercial product available from The Dow Chemical Company under thetrade name 6D65L, Tables 1 and 2, which has been compounded with anadditional 2000 ppm of ADK NA 11.

*The Flexural Modulus results listed in Tables 1 and 2 for the Resins ofExamples 7b-10 and Comparative Examples 7, 10a, and 10b were obtained inaccordance with test method ASTM D790-00, except the samples wereallowed to age for two weeks prior to testing.

TABLE 1 ASTM ASTM Melt Flexural Flow Rate, Xylene ASTM D Modulus, 1% GPCg/10 min. @ Insolubles, Nucleating 1003 Haze Secant, psi Mw/Mn GPC Mw230 C./2.16 kg wt. % Agent, ppm % Example 1 336,000 4.5 426,000 1.7 99.1ADK NA 21 11, 1500 Example 2 349,000 5.0 322,000 4.9 98.9 ADK NA 21 11,1500 Example 3 338,000 5.3 180,000 49.7 98.1 ADK NA 21 11, 1500 Example4 250,000 2.1 ADK NA 23 11, 1500 Example 5 330,000 4.5 426,000 1.5 99.1ADK NA 21 11, 830 Example 6 246,000 Not not 2.1 Not measured ADK NA 23measured measured 11, 820 Example 7a 234,000 3.2 99.0 MILLAD 3988, 500Example 7b 294,000* 4.8 314,100 3.0 98.5 ADK NA 18 11, 2000 Example 8263,000* 4.8 311,300 3.0 98.1 ADK NA 17 11, 2000 Example 9 215,000* 5.3319,900 3.0 97.3 ADK NA 16 11, 2000 Example 10 180,000* 4.6 312,600 2.896.8 ADK NA 15 11, 2000 Comparative 310,000 8.2 3.5 97.0 — — Example 1Comparative 350,000 11.8 13.8 98.2 Sodium 42 Example 2 Benzoate, 870Comparative 350,000 19.6 20.0 96.7 talc 49 Example 3 2000 Comparative242,000* 5.7 387,700 2 95.9 ADK NA 13 Example 7 11, 2000 Comparative180,000* 4.6 356,600 2 94.6 ADK NA 13 Example 10a 11, 2000 Comparative170,000* 4.5 296,600 4 93.9 ADK NA 15 Example 10b 11, 2000

TABLE 2 DSC Crystal- Ethylene lization DSC Melting DSC NMR Triad NMRPentad Material content, DSC Tg, Temp, Temp., Crystal- Pentad/TripadIsotacticity Isotacticity Description weight % Deg C. Deg. C. deg. C.linity % Ratio (%) % % Example 1 0 −3.80 133.8 168.4 73.6 99.84 99.0998.94 Example 2 0 −3.90 133.3 167.7 75.5 99.17 99.03 98.21 Example 3 0−4.60 133.5 166.0 75.4 98.49 98.24 96.76 Example 4 — — — — — — — Example5 0 Not 134.0 168.0 not 99.84 99.09 98.94 measured measured Example 6Not Not measured Not not not measured not measured measured measuredmeasured Example 7a 0.3 — — — — 98.87 97.6 96.5 Example 7b 0.6 Not 128.0162.1 67 98.66 97.1 95.8 measured Example 8 1.3 Not 127.1 158.9 67 98.5395.7 94.3 measured Example 9 2.0 Not 121.9 152.0 57 98.6 93.1 91.8measured Example 10 3.0 Not 117.4 146.8 54 99.12 90.7 89.9 measuredComparative 0 −4.98 126.0 165.2 70.3 99.22 97.98 97.22 Example 1Comparative 0 −6.51 128.0 164.3 72.8 98.58 97.98 96.59 Example 2Comparative 0 −4.27 127.5 163.1 71.3 98.62 96.95 95.61 Example 3Comparative 0.5 Not 129.0 161.2 59 97.5 92.1 89.8 Example 7 measuredComparative 3.0 Not 119.3 149.5 49 96.08 91.9 88.3 Example 10a measuredComparative 3.0 Not 119.1 148.0 46 95.5 89.1 85.1 Example 10b measured

Examples 11-17

Copolymers that are the same as the copolymers of Examples 7-10 (exceptthat different nucleator/clarifier additives ADK N21 and Millad 3988 areused) are produced. For the resins of Examples 11-17, Table III belowshows the values for Flexural modulus, haze, crystallinity, and meltingpoint. For Table III, the flexural modulus data were determined inaccordance with ASTM D790-00, except that the samples are aged for twoweeks prior to testing. As can be seen from Table III, NA 21 and Millad3988 operate similarly to NA 11.

TABLE III ASTM Melt Flow Rate, ASTM Flexural ASTM DSC DSC DSC Materialg/10 min @ Modulus, 1% D1003 Crystallization Melting CrystallinityNucleating Description Wt % E 230 C./2.16 kg Secant, psi Haze % Temp. °C. Temp. ° C. % Agent, ppm Example 11 0.6 3.0 284,000 25 124.8 161.4 60ADK NA-21, 2000 Example 12 1.3 3.0 251,000 24 122.2 158.4 60 ADK NA-21,2000 Example 13 2.0 3.0 204,000 18 117.5 150.5 53 ADK NA-21, 2000Example 14 3.0 2.8 169,000 15 114.2 145.6 53 ADK NA-21, 2000 Example 151.3 3.0 240,000 20 124.5 158.7 60 Millad 3988, 2000 Example 16 2.0 3.0208,0.00 14 120.4 151.4 64 Millad 3988, 2000 Example 17 3.0 2.8 171,00011 115.9 146.0 55 Millad 3988, 2000

Examples 18-21

A polypropylene copolymer of Example 7b, Tables 1 and 2, is produced inthe same manner as Example 7b, except that differing levels ofNucleator/clarifier were added to the base resin polypropylene copolymer(the matrix polymer), as indicated in Table IV. This base polypropylenecopolymer is compounded with several different impact modifiers toproduce impact modified copolymers as set forth in Table IV, Examples18-21, below. The impact modified copolymer final product is made byintroducing the impact modifiers as indicated in Table IV along with theother named additives are combined as described in the pelletizationdescription of Example 7. The impact modifiers listed are all Affinitypolymers having the tradenames designated in Table IV for Examples 18-21and are available from The Dow Chemical Company under the listedtradenames. All the Affinity polymers listed are substantially linearethylene/1-octene copolymers exhibiting narrow molecular weightdistributions.

TABLE IV Composition Units Example 18 Example 19 Example 20 Example 21Ethylene level in propylene- wt % 0.6 0.6 0.6 0.6 copolymer matrixAffinity Type PF 1140 PF 1140 PL 1850 PL 1280 Affinity level wt % 14 1414 14 Affinity Density g/cc 0.90 0.90 0.90 0.90 Affinity Melt Index 190C. g/10 min. 1.5 1.5 3.0 6.0 Clarifier type ADK NA 21 Millad 3988 ADK NA21 ADK NA 21 Clarifier level ppm 1500 1000 1500 1500 Properties at 23 C.Method Units Notched Izod Impact ASTM D256 A ft-lb/in 12.4 11.3 10.5 9.0Flexural Modulus @ 1% Secant ASTM D 790-00 psi 203,354 184,979 198,500203,433 Gardner Impact ASTM 5420 GC in-lbs 212 214 217 205 Average HeatDistortion 66 psi ASTM D 648 C 104 — — — Tensile Strength @ Yield ASTM D638 psi 4661 4557 4723 4712 Haze @ 1 mm ASTM D1003 % 18 25 17 15

Examples 18-21 show that the use of a highly crystalline polypropylenecopolymer of the invention as starting materials, together withethylene-alpha olefin impact modifiers, will provide impact modifiedpolypropylene copolymers that exhibit an excellentstiffness/toughness/clarity balance. Preferably, the impact modifiedcopolymers have a 1% secant flexural modulus of at least 170,000 p.s.i.,more preferably at least 180,000 p.s.i., further more preferably atleast 190,000 p.s.i., and in some instances, at least 200,000 p.s.i.Additionally, the impact modified polypropylene copolymers of theinvention preferably exhibit “no break” IZOD levels at room temperatureand at 0° C.; and preferably exhibit a ductile to brittle transitiontemperature (DBTT) of less than 10° C., more preferably less than 0° C.,further more preferably less than −5° C., and in some instances lessthan −10° C., even more preferably less than −20° C. Further, the impactmodified polypropylene copolymers preferably exhibit haze levels lessthan 25%, more preferably less than 20%, further more preferably lessthan 15%, and in some instances less than 10%.

1. A polypropylene homopolymer composition having a M_(w)/M_(n) of lessthan 5, a melt flow rate of less than 5 g/10 min, a 1% secant flexuralmodulus of greater than 300,000 psi, a pentad isotacticity of at least98%, a haze of less than 25%, less than 2% by weight xylene solubles,and a crystallinity of at least 75%, wherein the polypropylene resincontains 500 ppm to less than 2500 ppm of a nucleator/clarifieradditive.
 2. The polypropylene resin of claim 1, wherein thepolypropylene resin has an isotactic pentad/triad ratio of greater than95%.
 3. The polypropylene resin of claim 2 wherein the polypropylene hasa crystallization temperature of greater than 133° C.
 4. A polyolefincomposition, comprising: (a) A polypropylene homopolymer compositionhaving a M_(w)/M_(n) of less than 5, a melt flow rate of less than 5g/10 min, a 1% secant flexural modulus of greater than 300,000 psi, apentad isotacticity of at least 98%, less than 2% by weight xylenesolubles, and a crystallinity of at least 75%; (b) less than 40% byweight of an impact modifier having a density of from 0.885 g/ml to 0.91g/ml, wherein the polypropylene contains from 500 ppm to less than 2500ppm of a nucleator/clarifier additive and exhibits a value of haze ofless than 25%.
 5. The polyolefin composition of claim 4, wherein thepolypropylene contains from 650 ppm to 1500 ppm of a nucleator/clarifieradditive.
 6. The polyolefin composition of claim 4, wherein the densityof the impact modifier is within 0.01 g/ml of a density of thepolypropylene resin.
 7. The polyolefin composition of claim 5, whereinthe density of the impact modifier is within 0.01 g/ml of a density ofthe polypropylene resin.